Existing pest control methods differ for new build and retrofit installations. For example, currently, in new build installations control is achieved by use of a passive barrier. Conversely, in retrofit installations the common control method involves the use of chemical treatment. Failure of performance may occur in both of these common methods currently used.
In the case of a passive barrier, for example of the type disclosed in U.S. Pat. No. 5,417,017, even a very small failure can effectively have the same result as having no barrier at all, since termites are able to pass through very small openings. Consequently, 100% performance of a control method of this type is difficult to achieve for a new build housing installation. An additional problem with this method of pest control is that damage to the barrier may occur during work being undertaken subsequent to the initial installation, such that later alterations may damage the integrity of an existing well-fitted barrier.
The treatment of existing buildings when infested with termites generally relies upon the delivery of a fumigating chemical and/or pesticide to the total area of the underside of a building, where access is difficult. Consequently, the effectiveness of this fumigation method is reliant upon the operative's efficiency. It is unlikely that 100% of the termites will be killed on every such treatment, leaving some in place to continue damaging the building, which means that a further treatment is required periodically, for example every three months, which is a labor intensive as well as a costly procedure, and more importantly the building is gradually damaged more and more by the termites which are not killed off at each treatment as their population builds up again.
Various systems have been tried to keep termites at bay to protect buildings. Japanese publication document 11-036470 (Kagawa) describes a system in which a treatment agent (ozone) is delivered as a fumigation treatment in to an already-infested building with the intention of killing the insects in place in the building by applying a concentration of treatment agents sufficiently high for this purpose and for relatively short duration since, while such serious and potentially harmful fumigation is taking place in the building it is wise, if not downright necessary, for the building to be evacuated of its human inhabitants. Kagawa describes a treatment effected by infusing ozone for something in the region of two hours until the termites are killed.
U.S. Pat. No. 6,327,812 (Hedman) also relates to a fumigation treatment of up to six hours. In such fumigation treatments it is not possible to allow human habitation to continue. Another Japanese patent 6-3273902 (Miwazawa) involves utilizing a detector to sense the migration of termites in order to trigger the infusion of the treatment agent sufficient to kill the termites. This treatment is applied once the termites are in the building, and the aim of the treatment is to kill the termites entirely, although as discussed above, it has to be recognized that such total eradication is rarely actually achieved in practice.
An alternative approach is utilized in other circumstances, where it is known to utilize long term low level infusion of ozone, for example as described in U.S. Pat. No. 5,514,343 (Garbut), which keeps molds and bacteria at bay in animal housing. Similarly, U.S. Pat. No. 6,325,971 (Hayes) describes a system for distributing ozone throughout a poultry house, including the step of infusing a litter bed with ozone. The ozone is maintained at exposure levels lethal to pathogens within the litter bed indefinitely. The Garbut document describes the use of ozone in enclosed spaces, primarily fruit storage rooms or animal housing, with ozone being used to lethal effect on bacteria, fungus and molds. The document also refers to the maintenance of a residual amount of ozone sufficient continuously to suppress the bacteria, fungus and molds whilst being safe for human exposure to allow workers to move in and out of the ozonated area without hazard.
U.S. Pat. No. 6,276,304 (Tai) refers to the introduction of ozone beneath the ground, namely into the material within a manure pit beneath ground level constituting part of the interior of a pig raising house.
Although it is recognized in these documents that a low level of ozone may achieve the desired lethal effect while nevertheless being sufficiently low in concentration in the regions occupied by humans as to cause no damage to the humans, this system cannot be applied directly to the protection of buildings from termites as will be discussed in more detail below.
The performance of the delivery system therefore is the key to achieving effective control of termites. It has been found that in order to preserve the integrity of a building it is necessary to infuse the ground with a concentration of treatment agent which is sufficient to create a hostile environment without actually killing any termites. As a consequence the termites are unable to remain in the hostile environment and move away from it. Importantly, as they leave, they secrete a warning pheromone which acts as a deterrent to other termites, discouraging them from entering the protected region while it remains active. It is therefore not necessary to infuse the treatment agent into the protected region while their pheromone is active. Indeed, it has also been found that continuous, uninterrupted delivery of treatment agent such as ozone may even be counterproductive because it can mask the termites' own warning pheromone, and termites can get inured to the presence of the treatment agent and develop tactics to cope with its presence. One technique which has been observed is for termites to create tunnels from regurgitated cellulose obtained from wooden parts of the building's structure. The cellulose tunnels are impervious to ozone so that the termites are effectively screened from it and can consequently bore further into the timber weakening the structure despite the attempts to eradicate them. A prophylactic treatment thus requires a careful determination of the best concentration of treatment agent such as to cause the termites to vacate the protected region, rather than flooding the area and causing death without giving the insects an opportunity to escape since it is only upon escaping that they secrete their warning pheromone that is developed by the termites themselves to stick to the surfaces of their passageways and tunnels and warn other termites not to enter the protected region.